Solar cells convert solar radiation and other light into usable electrical energy. In a typical solar cell, solar radiation such as sunlight impinges on the solar cell and is absorbed by an active region of semiconductor material such as a film of silicon (Si) and/or gallium arsenide (GaAs), which generates electron-hole pairs in the active region. The electrons and holes may be separated by an electric field of a junction in the solar cell. It is this separation of the electrons and holes by the junction that results in the generation of a photocurrent.
The semiconductors often used as solar cell materials such as silicon and gallium arsenide typically reflect approximately 30% of the incident light that could otherwise participate in the generation of the photocurrent. The reflection losses of these photons may be reduced through the use of an Anti-Reflection Coating (ARC). A typical ARC is a layer consisting of the deposition of one or more thin film materials with carefully chosen thicknesses and refractive indexes. Oxide ARCs are commonly used in solar cell fabrication (Silicon oxi-nitrides, GaO, etc.). MgF2/ZnS is also often used as a double layer ARC for solar cells as it provides an ideal index match for cells with bandgaps ranging from 0.7-2 eV. An example of a conventional solar cell is shown in FIG. 1. FIG. 1 is a cross-sectional view of a solar cell consistent with certain conventional solar cells. Solar cell absorber 1 is provided with a glass or air layer 4. Between glass or air layer 4 and the solar cell absorber are typically two layers, for example, a thin film of ZnS, shown as ZnS layer 2 and a thin film of a MgF2, shown as MgF2 layer 3. Glass or air layer 4 may be comprised of any suitable substantially transparent substance known in the art for this application, including glass, or it may be comprised of air. The substantially transparent substance of glass or air layer 4 may affixed by such means as an epoxy or other suitable material.
These conventional methods of protecting solar cells suffer from a number of disadvantages. For instance, for conventional ARC schemes, a protective cover glass is needed to prevent premature aging of solar cells as a result of ARC degradation through weather effects, corrosion, and particle impact, for example. The addition of cover glasses, however, results in both optical losses and added manufacturing complexity and cost. In addition, some conventional ARC schemes may not be transparent over the entire desired range of the solar radiation spectrum. Accordingly, improved ARC schemes are needed to address one or more of the disadvantages of the prior art.